I'm sorry, but I disagree with you on one point, classic Twinkle from season 1 is nothing like the ultra stupid and brainless Twinkle from some (I said some!) episodes of season 2. She was naive, sure, but the Twinkle from season 1 would never have trusted Sharkbeard so easily, nor would she have thought Ruby was a virus or anything like that .
In "the convoy of honor", she quickly trusts the baron because he does his best to present himself as a good man, and since this is an early episode of the first season, we can assume they haven't seen much of him yet. Plus, she's not the only one charmed by his manner: the entire team is, except for Alex, who has known him well for years and knows what he's up to, and even he ends up being fooled.
Want another example? Okay!
In "I Am the King," it takes her so long to understand what happened because it wasn't that simple! Alex understood quickly because it's his father and because he's smart (it's Alex after all). Gene always analyzes everything, and Ruby spent time with the king (who was inside Fourchesac's body) in the dungeon. So it's normal that she gets it quickly too. But Twinkle? I mean, her friends didn't even bother to explain it to her, so it's understandable.
Of course, I could go on and cite all the episodes, but what I'm trying to say is that, sure, she can forget her wand somewhere or be clumsy enough to break it by sitting on it, sure, she takes seriously what her friends say when they try to trick a troll, but what matters is that she took the time to play with a lonely baby monkey in the jungle, she was the one who went into the mouth of a dragon just to retrieve the spellbook, even though it was disgusting and frightening, and that she was the only one who thought about the safety of a troll who was trying to eat them a moment before.
Twinkle has always been smart and thoughtful in season 1, she quickly figured out how to destroy the queen's statue, and she also was the one who solved the riddle of "All that glitters" for example.
It's just that she happens to be with Gene and Alex who are smarter in comparison, and Ruby who is strong and less emotional than her (I say this because people always tend to compare girls on these points which is stupid).
She has weaknesses like everyone else, but she also has strengths that distinguish her from all her friends, and that's what makes them a team: not everyone needs to be the same.
But I completely agree with you about her sassy side; she's seen and experienced a lot (we know our heroes have known each other for years in season 1), so it's perfectly natural that she developed this trait over time. But she kinda already had that side in the first season, it wasn't just as pronounced as in season 2.
She's become more self-assured and isn't intimidated anymore; the rest of the time, she can be herself, sweet and silly.
And I don't think feminine characteristics are a problem; stereotypes and archetypes are great! Ruby is the typical tomboy who hates girly stuff, Gene is the smart, quiet boy, Alex is the classic hero, and Alien is the cute mascot. But that's just the surface; they can be so much more!
The problem is that season 2 has an unfortunate tendency to flanderize the characters (this is a recurring phenomenon in all media), and Twinkle is unfortunately the one that has suffered the most.
For example, in "A Pirate's Honor," Ruby looked at her when everyone was against her because she trusted Twinkle the most and didn't want to lose her trust.
But then there's "A pirate virus" in season which I mentioned earlier (I hate this episode and I'm not going to make a gif of it).
She has literally become a caricature of herself! I cannot blame anyone for forgetting these aspects of her, because even the authors have forgotten them (or they never knew about them). It's as if they have reduced her to her bare surface, nothing more, which is a real shame.
I think it's important (especially in children's cartoons) to show that being sensitive and kind is essential and doesn't mean being weak. It's a real shame that the characters who possess these qualities are also the ones portrayed as stupid, what would children think?
Twinkle is a wonderful character and I think she deserves more love !!